Humans immediately place things they see (including other people) into various categories based on stereotypical precepts. Humans have also used animals as de-facto examples of stereotypes for at least as long as there has been written language.
Who hasn't been asked as a child: "If you could be any animal, what animal would you be, and why?" Apart from the interesting bit that you almost never hear a child say "I'd like to be a human, because they have the ability to use tools, create new things, and have developed ways of storing knowledge about how to survive separate from genes." Is the other interesting bit that indicates that, at least as children, we all would like to be more animal than human ... able to swim better, see better, run faster, fly, etc.
This, I think, is the very heart of the matter. The symbolism of animals and their stereotypical properties are pervasive in nearly every culture on the planet. Used as examples for how to live (or not to live), used to evoke response in advertisements, used in entertainment and religion... probably the only thing more ingrained into our collective consciousness than our place in and relationship with the rest of the animals on our world, is our preoccupation with procreation.
Being a family friendly forum, I'll not ponder publicly on the predictable pre-disposition of people's propensity for producing ... less socially accepted forms of art.